The present invention relates to an analytical method and an analytical apparatus which use a capillary tube and especially to an analytical method and an apparatus suitable for measuring samples or analytes separated in a capillary tube for separation.
Separation analytical methods such as the electrophoretic method and chromatography are widely used for analyzing and measuring a slight amount of substance contained in liquid or gas test samples. Recently, capillary tubes have been employed as a means to carry out separation of a sample in these separation analytical methods in order that a substance contained at low concentration in a slight amount of sample can be measured.
Various detection methods have also been proposed in gas chromatography and liquid chromatography for detection of analytes separated by a separation capillary tube. Especially, research on a new detection method has been effected in capillary-zone electrophoresis (hereinafter referred to as "CZE"). For example, a capillary-zone electrophoresis which detects the separated analytes by placing a work electrode of an electrochemical detector downstream the separation capillary tube is disclosed in "Analytical Chemistry", vol. 61, pp. 292A-303A (1989). Furthermore, a capillary-zone electrophoresis which measures thermal changes based on the sample in a capillary tube using a probe beam by irradiating the separation capillary tube per se with an excitation laser beam and a probe laser beam is disclosed in "Applied Spectroscopy", vol. 43, pp. 196-201 (1989).
According to the method which uses a conventionally generally employed detector, the analyte separated by capillary tube is led to the detector through a flow path and there occurs reduction in resolving power for separation of analyte because the analyte is taken out of the capillary tube.
Furthermore, in the method of the first reference cited above, since a high-voltage current source necessary for separation operation and a detection system must be electrically isolated, a connection structure comprising a porous glass provided between the outlet end of separation capillary tube and the inlet end of flow path in detection system is employed and thus, resolving power unavoidably reduces owing to the presence of the connection part. Furthermore, detection sensitivity is not sufficient. The method of the second reference cited above employs a construction which detects a change in refractive index caused by expansion of the sample liquid per se which undergoes thermal change by excitation beam and, besides, detects the probe beam which has passed through the sample in the capillary tube. Therefore, the measured value is affected by scattering and reflection of the probe beam at the surface of capillary tube.